Zea mays, commonly known as maize or corn, is a grain important both as human food and as animal feed. Maize seeds or kernels are naturally low in lysine content due to its protein composition. The majority of maize seed proteins are the zeins or prolamins, which are found in the endosperm and account for more than half of the total seed proteins. Zeins or prolamins are rich in proline, alanine and glutamine, but almost completely devoid of the essential amino acids, lysine and tryptophan. Due to the relative abundance of zeins, the contribution of lysine and tryptophan from other seed proteins is diluted. Exogenous lysine is often added to animal feed as a necessary supplement. It is therefore of interest to increase the level of lysine in maize seed.
Amino acid levels in transgenic plants can be manipulated by various genetic techniques, including, but not limited to, modification of endogenous gene expression and/or expression of exogenous recombinant DNA in the transgenic plant. Coordinated decrease and increase of gene expression of more than one gene using transgenic constructs is disclosed in U.S. Patent Application Publication 2004/0126845. Methods and recombinant DNA constructs useful for producing anti-sense-oriented RNA for gene suppression in transgenic organisms are disclosed in U.S. patent application Ser. No. 11/057,062, published as U.S. Patent Application Publication No. 2005/0176670A1. U.S. Provisional Patent Application No. 60/638,256, discloses DNA cassettes for suppressing at least one gene in a cell of a eukaryote, such DNA cassettes comprising a promoter operably linked to transcribable DNA including at least an intron, a polyadenylation signal, and a polyadenylation site, where there is embedded in the intron heterologous DNA which is derived from at least one gene targeted for suppression and which is transcribable to RNA capable of suppressing the at least one gene. All of these referenced patent applications and publications are incorporated by reference in their entirety herein.